The present invention relates to a compact image pickup module that is attached to a mobile telephone or a PDA with a photographing function or the like, and a lens unit suitable for a compact image pickup module or the like, and more specifically to a compact image pickup module that is capable of performing appropriate focusing, preventing inclination of the optical axis of an imaging lens with respect to an image pickup element such as a CCD sensor, and performing alignment of the image pickup element such as a CCD sensor with ease, a compact image pickup module where macro photographing is realized with a simple mechanism, and a lens unit that includes multiple lenses and is capable of preventing displacements between the optical axes of the lenses.
A compact image pickup module installed in a mobile telephone, a PDA (Personal Digital Assistant), a compact digital camera, or the like is ordinarily constructed by combining an image pickup element (such as a CCD sensor or a CMOS sensor; hereinafter the CCD sensor will be described as a representative), a holding member (hereinafter referred to as “CCD holder”) that holds the CCD sensor, an imaging lens (hereinafter also simply referred to as “lens”), and a cylindrical lens-barrel that holds the lens.
Such a compact image pickup module generally uses a CCD holder having a through hole and is assembled by fixing a CCD sensor to one end of the through hole, accommodating a lens-barrel holding an imaging lens from the other end of the through hole, and fixing the lens-barrel.
More specifically, as is well known, screw threads are cut into the inner wall surface of the CCD holder and the outer wall surface of the lens-barrel and are caused to mesh with each other. Then, focus adjustment (focusing) is performed by adjusting a distance between the light receiving surface of the CCD sensor and the imaging lens through adjustment of the screw-in amount of the lens-barrel. After the focus adjustment is performed, the CCD holder and the lens-barrel are fixed to each other using an adhesive or the like when the compact image pickup module is a fixed focus module.
Also, as a result of technological advancement in recent years, the image pickup element, such as the CCD sensor, has a highly reduced size and increased resolution. Therefore, the imaging lens (lens unit) applied to the compact image pickup module is also required to have resolving power with which it is possible to separate thin lines at a level of 150 to 200 [lp/mm] from each other. That is, an imaging lens having such high resolving power needs to be used as the imaging lens.
It is difficult to realize an imaging lens (lens unit) having such resolving power using a single lens. Therefore, an imaging lens (lens unit) having intended resolving power or precision is ordinarily realized using a combination lens obtained by combining multiple lenses with each other.
As schematically shown in FIG. 11, such an imaging lens (lens unit) produced by combining multiple lenses with each other ordinarily uses lenses 100 (100a, 100b, and 100c) having mutually different outer diameters and a lens-barrel 102 obtained by forming a lens holding portion, whose size is changed stepwise so as to correspond to the respective lens diameters, and is constructed by incorporating the lenses into the lens-barrel 102 in the order of the lens 100c, the lens 100b, and the lens 100a in accordance with the lens diameters and fixing the lenses 100 to the lens-barrel (see, for example, JP 2002-82272 A).
As a matter of course, in order to obtain a high-quality photography image, it is required that the imaging lens is fixed so that the optical axis of the imaging lens, that is, the lens-barrel is not inclined with respect to the light receiving surface of the CCD sensor.
When the optical axis is inclined, an imaging surface is also of course inclined, so a photographed image is not appropriately formed on the light receiving surface of the CCD sensor and image quality is degraded.
As described above, however, in the conventional compact image pickup module, the screw threads of the lens-barrel and the CCD holder are caused to mesh with each other, focus adjustment is performed by adjusting the screw-in amount, and then the lens-barrel and the CCD holder are fixed to each other. With this construction, gaps inevitably exist between the screw threads, so the lens-barrel is inclined and the optical axis of the imaging lens is inclined.
As described above, the CCD sensor has a highly reduced size and increased resolution due to the recent technological advancement and therefore an imaging lens having high resolving power, with which it is possible to separate thin lines at a level of 150 to 200 [lp/mm] from each other, is used as the imaging lens applied to the compact image pickup module. Therefore, when the optical axis is inclined, even if the degree of the inclination is small, there occurs extremely significant image quality degradation.
Also, in recent years, there are many cases where a compact image pickup module installed in a mobile telephone has a so-called macro photographing function that enables photographing in a close range or photographing of a small object by changing a photographing distance through movement of an imaging lens from an ordinary position toward the front (toward a subject).
In general, however, many components are used to realize the macro function (for instance, multiple springs are required) and the macro function also has a complicated structure, so a compact image pickup module where the macro photographing function is realized using a simpler construction is desired.
Further, in a like manner, as a matter of course, in order to obtain high-quality photography images with stability, it is required that positioning of the CCD sensor has been performed so that the optical axis of the imaging lens and the center of the light receiving portion (light receiving surface) of the CCD sensor appropriately coincide with each other.
In the compact image pickup module, for instance, the CCD sensor is incorporated into the CCD holder by performing rough positioning in a direction (hereinafter referred to as “x-y direction”) orthogonal to the optical axis of the imaging leans through abutment of an end portion of the CCD sensor in the x-y direction against a reference portion provided for a sensor holding portion formed for the CCD holder.
Here, generally, accuracy in positional relation between the outer surface and the light receiving portion of the CCD sensor is in no way high. Consequently, when the positioning of the CCD sensor in the x-y direction is performed in the manner described above, it is impossible to perform the positioning of the CCD sensor in the x-y direction accurately so that the optical axis of the imaging lens and the center of the light receiving portion coincide with each other.
Therefore, in course of manufacture of the compact image pickup module, after the rough positioning in the x-y direction is performed using the outer surface in the manner described above, fine positioning in the x-y direction is performed so that the optical axis of the imaging lens and the center of the light receiving portion of the CCD sensor coincide with each other by taking a reference image and adjusting the positions of the lens-barrel and the CCD sensor while viewing an image obtained through the photographing. Following this, the CCD sensor is fixed to the CCD holder using an adhesive or the like.
Such CCD sensor incorporation work takes a very long time and is a factor of a reduction in productivity of the compact image pickup module and an increase in manufacturing cost thereof. In addition, with such positional adjustment in the x-y direction based on images obtained through photographing, there is also a case where stable manufacture of products of appropriate quality where the optical axes of imaging lenses and the centers of light receiving surfaces of CCD sensors coincide with each other becomes impossible depending on the skill of an operator, the precision of an adjustment jig, or the like.
Further, in a like manner, as a matter of course, in order to obtain a high-quality photography image, it is required that the optical axes of the lenses 100 incorporated into the lens-barrel 102 appropriately coincide with each other. In particular, in the compact image pickup unit, the imaging lens is required to have high resolving power as described above. Therefore, when displacements (hereinafter referred to as “inter-lens eccentricity”) between the optical axes of the lenses 100 occur, even if the degrees of the displacements are small, there occurs extremely significant image quality degradation.
Between the lens-barrel 102 and the lenses 100, however, gaps (clearances) for incorporating the lenses 100 into the lens-barrel 102 exist, so the incorporated lenses 100 move in the lens-barrel 102 and the inter-lens eccentricity occurs.